The present invention relates to high speed data interfaces in general, and more particularly to training a phase shift circuit used in a high speed interface.
In some high speed interface circuits, for example double data rate memory interfaces, a strobe signal is used for the timing and recovery of a number of data signals. That is, a transmitting circuit provides a number of data signals as well as a data strobe signal to a receiving circuit. This strobe signal may be transmitted such that its edges are aligned to edges or transitions of the data signals.
However, for proper data recovery, it is desirable for the strobe to be phase shifted relative to the received data, for example by ninety degrees. It is also desirable that this phase shift be done accurately to improve data recovery. It is further desirable that this shift be made automatically, for example at device power up or other appropriate time. By being made automatically, problems associated with manual adjustment, such as operator and other errors, are reduced or eliminated.
Thus, what is needed are circuits, methods, and apparatus for providing adjusting a phase shift in a high speed interface circuit. It is also desirable that this adjustment or training be performed automatically.